How The Slide Rule Got Us To The Moon

My father is 66 years old. He grew up in a time that people today tend to easily forget. In reality, it wasn’t long ago at all.

Modern technology has made us believe that anything is possible. Artificial intelligence, quantum physics, and human augmentation are in the realm of human understanding because of the power of computers. But Dad didn’t have one of those growing up.

Nobody did.

People my age grew up in a time when technology was improving so quickly, buying an phone meant one half the size with twice the power would be available a few months later.

Dad always reminded me of how lucky I was by telling me what the greatest technological achievement of his youth’s generation was:

“We put a man on the moon using only a slide rule. That’s pretty amazing.”

And it’s true. With the technology available at the time, the challenge is almost unimaginable.

In its simplest form, the slide rule adds and subtracts lengths in order to calculate a total distance. But slide rules can also handle multiplication and division, find square roots, and do other sophisticated calculations including solving trigonometric and logarithmic problems.

We used those calculations to fling human beings out of our atmosphere and onto a foreign object floating in the vacuum of space.

If we sent astronauts to the moon today, #moonlanding wouldn’t even be trending on Twitter.

But in 1969, when the most advanced technology we had was a piece of wood and metal, it was arguably the greatest scientific and mathematical achievement in the history of mankind.

When we launch a rocket, physics and gravity become our biggest enemy. We have to take a few major things into account:

The planetary motion of both the Earth and the Moon. The Earth goes around the sun at a brisk 66,000 miles per hour, so the calculation of when and where to launch can get complex.

The rocket needs to build enough force to overpower Earth’s gravity, no easy feat. Millions of pounds of thrust are required to escape the atmosphere.

Getting that thrust requires a very high degree of controlled explosive energy. There’s a fine line between exploding in one direction instead of simply exploding.

But that’s just the very start of a list of things that could complicated a launch. A rocket is an extremely complex device. There are millions of pieces and therefore millions of opportunities to make errors, both in calculation and construction.

The combination of the mechanical challenges of a successful launch and the technological challenges of spacecraft operation make success in space missions one of the hardest of human endeavors to achieve.”

— John Logsdon, Space Policy Expert

Traveling through space correctly is no cake walk either. Ensuring that the space craft leaves Earth in a manner that will allow them to predictably travel the 238,900 miles (give or take) of frozen, vacuous space and land on a hospitable patch of Moon is an immense calculation in itself.

These challenges exist for brilliant rocket scientists today, regardless of the computing power available with the click of a mouse.

Then there’s landing on the moon, which brings it’s own set of complications:

In just 12 minutes, Armstrong and Aldrin had to bring their lunar module Eagle from a height of 50,000 feet, orbiting at a speed of several thousand miles per hour, down to the surface in what amounted to a controlled fall.

Alarm tones in the astronauts’ headphones signaling the onboard computer, which controlled Eagle’s speed and orientation, becoming overloaded with tasks (this actually happened during the Eagle’s decent to the Moon’s surface).

On July 16, 1969, Apollo 11 astronauts Neil Armstrong, Buzz Aldrin and Michael Collins mounted a three-stage 363-foot rocket. At 9:32AM EST, the engines fired and Apollo 11 engines used 7.5 million pounds of thrust to propel towards the emptiness of space.

About 12 minutes later, the crew was in Earth orbit. On July 19, after Apollo 11 had flown behind the moon out of contact with Earth, came the first lunar orbit insertion maneuver. 102 hours and 45 minutes into the mission, partially piloted manually by Armstrong, the Eagle landed on the Moon’s surface in an area known as the Sea of Tranquility.

The fact that this was successfully pulled off almost 50 years ago by mathematicians and physicists on sliding pieces of wood is beyond belief.

Upon his return, Neil Armstrong’s comments convey his awe of how tens of thousands of people made this possible.

In my view, the emotional moment was the landing. That was human contact with the moon, the landing…. It was at the time when we landed that we were there, we were in the lunar environment, the lunar gravity. That, in my view, was…the emotional high. And the business of getting down the ladder to me was much less significant.”

Every guy that’s setting up the tests, cranking the torque wrench, and so on, is saying, man or woman, ‘If anything goes wrong here, it’s not going to be my fault.’”

Our dreams of the present were build on those from the past. Today’s generations should stand in awe of what previous generations did with so few of the technological resources we take for granted.

To all those who slid wood together to get us to the Moon, we salute you.